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W. G. HAHTWIG.

THERMOSTAT. APPLICATION FILED |ULY1!.19|8.

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APPLICATION FILED lUlY 1l. 1918.

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UNITED STATES PATENT OFFICE.

VWIIJILIIAIMG'. HARTWIG, OF CHICAGO, ILLINOIS, ASSIGNOR TO RAILWAY UTILITY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

THERMOSTAT.

Specification of Letters Patent.

Patented Aug. 9, 1921.

Application filed July 11, 1918. Serial No. 244,495.

To aZZw/Lom'z't may concern:

"Be-it known that I, IVILLIAM G. Haar wie a citizen of the United States, residing at h'icago, in the county of Cook and State ofpIllinois, have invented certain new and useful Improvements in Tlfiermostats1 of which the followingis a specification.

.My invention relates more particularly to thermostats for controlling the temperature in'ftherooms of buildings, street and other railwayv conveyanees, and in general in apartments-where it is desired to maintain Va fairlyuniform temperature. There are two'fformsfof thermostats in common use. one Iofrivvhich depends on the difference Vin Yexpansion,under similar changes of temperature ,of two metals7 4the mechanism employed commonly involvinga strip or bar lcomposed of twg longitudinal strips of the respective metalsgvhmhbar because of its composition bendsK under change of temperature, the movement of the bar being used to control someorm of heat supplying device. The

i ther ncommon form of thermostat referred toaboyejcomprises a mercury column, similartor.'thermometer,.which rises and falls ivvithf'iehangesin fftemperature to ,close and openffa' ele'ctric circuit controlling some form ofheating apparatus My invention iswapplicable to either of these two forms of thermostat and has for its object to increase. the delicacy and accuracy thereof and also to renderA the instrument less liable to damage -and to being tampered with, and to make it 1es'Sobtrusive .and more adaptable to dif- In the thermostats of the prior art, whether of the one type or the been considered and was in fact necessaryfthat freier access of the surrounding'ratmiosphere to the sensitive member of the thermostat be provided for in order that the instrument should respond promptly to sufliciently small variations in temperature.

Therefore it was necessary to mount the 1n- `strur`nent in an open case which not only "ermitted access of dirt, dust and moisture to affect the parts and theirrmechanical but permitted easy access to any one desiring to tamper with the instrument.

This latter characteristic was particularly unfortunate because those unfamiliar with .the construction and operation would fre iquently in their endeavors to regulate the instrument, apply tools thereto in such a way as to break or otherwise injure the apparatus. According to my invention the thermostat is completelyinclosed and in fact may be hermetically sealed within the case excluding dirt and moisture and preventing tamperingr with the device. At the same time the instrument is rendered much more sensitive than former devices of the same kind. In its broader aspect the invention consists in furnishing the instrument with a heat interchanging element of extended surface for Contact with the latmosphere of the apartment, the temperature of which is to be regulated, and which is adapted to communicate heat from the atmosphere to the sensitive element of the thermostat or vice versa so that the latter more readily responds to changes in atmospheric 'temperature. Preferably, the heat interchanging element forms a part of the inclosing case for the thermostat and incase great accuracyY is desired. it may be heat insulated from the support so as to exchange heat only with the atmosphere. Other features of the invention will be understood from the following specification in which I have described in detail two preferred forms of the invention. It is'to be understood however, that the specific disclosure is for the'purpose of exemplification only and thatthe scope'of the invention is defined in claims in which I have endeavored to distinguish it from the prior art so far as known to me without, however, relinquishingr or abandoning any portion or feature thereof. 1

Referring to the drawings, Figures 1, 2 and fi illustrate respectively a perspective view of the entire instrument, a similar view on a larger scale of an instrument with a portion thereof removed, parts beingr shown in dotted line, and a longitudinal section of my invention as applied to a thermostat of thc thermometer or mercury type; and Fig. 4 is4 a longitudinal section on an enlarged the following merrury| column within. The purpose of these wires is to close an electric controlling circuit when the thermometer mounts sniliciently high in the tube` The terminals for wires 8 and 9 are shown at 10, 11 respectively. One of the objections which is most frequently urged against the mercury thermostat is the delicacy of the glass tube thereof which is quite liable to breakage by rough handlingy and shock, much of the trouble arising from the fact that the heavy mass of mercury causes a hammer on the tube whenever the latter is jarred. In order to olivi-ate or minimize trouble from this source the sensitive clement is mounted upon springs 12, 13, which as shown Span the hollow 7 of the base and support the tube out of contact with the latter- Preferably the springs are arranged at an incline to the axis of the base to cushion the latter 'from shock either transversely or longitudinally of the base.

As shown more particularly in Figs. 2 and V3 the thermometer thermostat is attached to the respective springs by means of double clampingr coils 26, the coils of which are connected by an intermediate loop 27 which engages the spring to which it is connected as shown in Fig. 3.

Even when completely exposed to the atmosphere the sensitive element or thermometer tube 6 presents a very limit polished surface of Contact and therefore responds but slowly to changes in atmosphere temperature.

In order to provide for the more rapid interchange of heat between the sensitive element and the atmosphere I provide a heat interchange element 14 which in the present instance takes the form of a thin flat plate of heat conductive material, preferably metal. For this purpose the more conductive metals are preferably employed and I lind copper, silver and aluminum especially adapted to produce the desired result. Preferably the element is in the form of a thin sheet of metal and is in heat conductive relation with the sensitive element of the thermostat. In thc particular foi-1u shown this relation is maintained by a clip or clamp 15 which is struck up from a thin metal plate, the base 1G of which is soldered, or otherwise secured to the heat interchange plate and the gripping membersA 17 of which are bent to hear upon the tube of the thermometer, on opposite sides of the bulb containing thc bulk of the mercury therein. The heat interchange element 14 has a much more extended surface than the tube G and is also by reason of its material much better adapted to exchange heat with the atmosphere, and therefore it assists very largely in speedily reducing differences of temperature between the sensitive element and the atmosphere. lf desired the instrument may he used \vith out an inclosure. But for most purposes,

as for example in connection with the hearing system of cars or rooms, it is desirable to inclose the sensitive element to protect it from dirt and moisture and injury from improper handling. Therefore an inclosure or container for the instrument may be completed by adding a surrounding wall 18 beween the heat interchange plate and the base. Preferably wall IS is formed of a material of much lower heat conductive Capacity than the in terchange plate and l have found that for most purposes if copper or other highly con ductive metal be used for the heat interchange element iron may be used for lthe wall 18, its heat conductive capacity being very. much less than that of copper; Other materials than metal may be used for this pjurpose, however, if desired. The Wall 5 might be made of the same material as. the plate 14, but in this case the instrument would not be quite so accurate because of the interchange of heat with the support. f a less conductive metal than copper be employed for the heat interchange plate it becomes for obvious reasons desirableto eml heat conductive material than iron for the Wall 18, and preferably some non-metal is substituted. I have shown the wall 18 as provided with a flat ange 19 and depending skirt 2O edge of the base 5, non-essential. l,

vIn Fig. f1 as above stated, I have 'shown my invention as a pliedl to a mechanical t ermostat. y That illustratedvis of a type so vvell known that it is unnecessary to describe the same in detail. It issufficient to observe that the base of the instrument is shown at 22,this ele- 21 and the sensitive element at.

osed of superimposed strips ment being com of two metals o widely different coeilicients of expansion. The heat interchange plate be substantially the same Q3 and Wall 24 may as those described in connection with the but obviousliythisf isfa other modification of the invention and act in the same manner. In order to effect the conduct of heat between the sensitive element '2Q and the heat interchange plate 213 I provide the latter with a series of thin springs 25 of heat conductive material'. which springs, however, are so light that they. do not materially affect the movement o` the bar or heat sensitive element 22 under changes of temperature. i

As above stated the casing may be hermetically sealed if desired and in-any event is ordinarily closed against dnstand tampering by an unauthorized person. Obviously the form of the casing may be any desire( and if preferred into a recess formed in the Wall of the compartment to conceal the same. the sensitive plate being in the plane of the surface of the wall and if desired colored to correspond thereto.

for fitting varound the the instrument may be let I claim:

l. A thermostat comprising a base, ametal cover, secured to the base and forming a substantially closed chamber therewith, a thermostatic element mounted in said chamber and a heat conducting element in contact with the cover and with the thermostat element.

2. In a device of the class described, a base, a hollow cover mounted on the base secured thereto and forming with said base a substantially closed chamber, a thermostatic element mounted in said chamber, a heat conducting element in conductive relation to the hollow cover and to the thermostatic element, und electrical connections extending through the base and connected to said thermostatic element.

3. In u device of the class described, a base, a. metallic cover supported on the base and forming therewith a closed chamber, a thermometer-thermostat supported in said closed chamber and protected thereby from tampering and a heat conducting element in heat conductive relation to said cover :1nd thermometer-thermostat.

WILLIAM G. HARTWIG. 

